S.I.Cameron wrote: > > Milton, Euan, all: > > Has anyone ever seen an estimate of the number of rotations of removing > the dominant trees (= 'best' genes) it takes before the genetic base of > a repeatedly intensively logged area becomes impoverished. Viewed > strictly from a tree improvement perspective, plantations, wherein new > and presumably superior provenances are imported, should show increased > "sustainability" over time according to the definition below, provided > no site degradation occurs. > > Stewart > > fore057 wrote: > > > > > To me, a "sustainable" system is one which allows people to make > > >use of the resource at the same level in future generations, say into the > > >seventh generation yet to come. Michael Pilarski's book, _Restoration > > >Forestry,_ argues that plantation forestry suffers from declines in > > >productivity starting in about the third rotation. Hence, plantation > > >forestry is not "sustainable." > > > Milton Takei > > > Eugene, Oregon, USA > > > <miltont@efn.org> Because many people besides myself are grappling with the issue/topic/definition of "sustainability", I'm offering a few comments...correction, "ruminations", which may or may not be correct. There are others out there that certainly know more about this than I do, so I hope to learn from them. First, I've always wondered if "dominant" trees *necessarily* have the best genes. It seems to me that most dominant trees in a stand are big because of happenstance. They were at the right place at the right time. A local disturbance released them from competition, whereas their nearby neighbors may not have been. Or microsite variation provided one tree slightly more moisture or nutrients that became critical during stress periods--other trees did not have this stress protection. Basically, dominant trees have lived a relatively "charmed" exisitence, one might say. Certainly, genes play a part--as they do in all aspects of biology--but, I think that I'd wager my gene-impoverished tree in the *right* location against your super tree in a low-light, high-competition, poor-microsite location anyday. Sounds like the old "genes vs. environment" argument. Second, I too would like to see specific scientific evidence supporting the hypothesis that there is loss of growth on plantations after several rotations. I have heard/read this before, but don't recall ever seeing any evidence. And I just saw a synopsis of a European Forest Insitute report saying that growth in European forests was increasing, although no details of the study data were included. I'm confused by all of this. Third, even though I haven't seen the evidence to support this conjecture, I'm inclined to believe it. The reason that I'd do so is that with each removal of wood from the site, there is a tremendous loss of carbon. This is carbon that would otherwise have gone into the organic matter pool of the soil. It is there that micro-organisms and other processes turn that OM into nutrients for plant growth. So, after several rotations (with their concommittant removal of carbon) the OM and micro-organism stores of the soil become depleted to the point that trees no long grow as well as before. Certainly, improved genotypes provided by plantation stock can make up for this growth, at least in the short term. But, for how long can they make up for a continually declining soil nutrient generating capacity? Any logging is going to remove some carbon and deplete the soil to some extent, we just have to find out what level of logging and soil depletion can be sustained. Soil is both "sink" and "source" in the forest. It's seems pretty obvious that we can't in perpetuity remove something from the souce without balancing that removal with a similar reinvestment. And, I'm sure that everyone knows that fertilization is not part of sustainability, so it's not part of the solution. If I've stated something utterly wrong here, I welcome correction. These things bother me and I would like to understand them better. DAN -- ==================== mailto:schmoldt@vt.edu ======================== Daniel L. Schmoldt Brooks Forest Products Center USDA Forest Service Virginia Tech (540)231-4674 (FAX 8868) Blacksburg VA 24061-0503
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